1. Field of the Invention
The present invention relates to a novel light-sensitive composition containing a compound capable of forming free radicals by irradiating with light and more particularly to a novel light-sensitive composition containing a light-sensitive s-triazine compound.
2. Description of the Prior Art
Compounds which are decomposed by the irradiation with light and thus form free radicals (free radical generator) have been well known in the field of graphic arts. They have widely been used as a photopolymerization initiator in a photopolymerizable composition, a photoactivator in a free radical photographic composition and a photoinitiator for a reaction which is catalized with an acid formed by irradiating a component with light. With using such a free radical generator, it is possible to form a variety of light-sensitive materials which are useful in the image-forming systems such as printing, duplication, copy or the like.
Organic halide compounds are photolytically dissociated to provide free radicals of halogen such as chlorine free radicals and bromine free radicals. These halogen free radicals act as a good hydrogen atom-extracting agent and form an acid if a hydrogen donnor is present. As to the application of these organic halogen compounds to photopolymerization processes and free radical photographic processes, reference is made to--Light Sensitive Systems--, by J. Kosar, 1965, pp. 180-181 and 361-370, J. Wiley & Sons (New York).
Typical examples of such compounds capable of forming halogen free radicals by the action of light includes carbon tetrabromide, iodoform and tribromoacetophenone and they have widely been used. However, these free radical generators suffer from a drawback that they are decomposed only by light having a wave length of a quite narrow range. In other words, they are sensitive to light in the ultraviolet region having a wave length shorter than the principal wave length of light sources commonly utilized. The organic halogen compounds conventionally used are thus inferior in the capability of generating free radicals since they cannot effectively be decomposed with light of from near ultraviolet to visible regions emitted from the light sources generally used.
In order to eliminate such a disdvantage, it has been proposed to extend the wave length range to which they are sensitive by admixing them with a certain sensitizer. For instance, as such sensitizer, U.S. Pat. Nos. 3,106,466 and 3,121,633 disclose merocyanine dyes, styryl bases and cyanine bases. The addition of such a sensitizer makes it possible to extend the wave length range, to which these organic halogen compounds are sensitive, to visible region, however, the sensitivity thereof is still insufficient in the practical point of view. In general, the sensitizer should be selected from those having a good compatibility with free radical generators and other components incorporated in the light-sensitive compositions. Nevertheless, it has generally been difficult to select sensitizers of good compatibility and high sensitivity.
Under such circumstances, halogen free radical generators, which are sensitive to near ultraviolet to visible regions, have been proposed. Examples of such generators include halomethyl-s-triazine compounds such as those disclosed in U.S. Pat. Nos. 3,954,475; 3,987,037 and 4,189,323. The wave length range sensitive to these compounds is between near ultraviolet and visible regions, however, they do not effectively utilize the light irradiated because of relatively low sensitivety to photodecomposition. In addition, these triazine compounds cause crystallization in the light-sensitive compositions during long term storage which leads to the reduction in the sensitivity.